1. Field of the Invention
The present invention relates generally to bioconversion of animal waste to useful products, and more particularly, but not by way of limitation, to methods of treating poultry manure using thermophilic anaerobic digestion.
2. Brief Description of the Art
The present invention is directed to methods for treating manure which involve anaerobic digestion. Conventional anaerobic digestion technology has certain limitations in terms of reaction rates and the ability of the bacteria to be productive when conditions (such as pH, temperature and concentration of certain chemical constituents) in the digester are not optimum. The anaerobic digestion process depends on a collection of bacteria collectively known as anaerobes, and such bacteria systematically break down organic material into simple molecules.
The conversion of animal waste into useful products such as methane and fertilizers using anaerobic digestion is a well established technique in theory and practice. Numerous farms in the United States and around the world are now successfully capturing methane gas that is released from either an anaerobic digester or a covered lagoon. The gas produced is generally utilized to generate electricity or combusted to provide heat for local operations. The majority of such projects are located on swine or dairy operations. Some efforts have been made to adopt such conversions to poultry operations, with most such efforts directed to egg laying poultry and virtually none to broiler operations.
One example of such effort for egg-laying poultry operations is found in U.S. Pat. No. 6,521,129 B1 (“U.S. Pat. No. 6,521,129”), the entirety of which is incorporated herein by reference. In U.S. Pat. No. 6,521,129 the prior art methodology of dilution of the difficult to treat poultry manure was recognized, as well as the potentially inhibitory parameters of digester temperature, oxygen or air intrusion, pH fluctuation, and build up of toxic constituents such as ammonia, hydrogen sulfide or excess volatile fatty acids. The solution in U.S. Pat. No. 6,521,129 was to add raw material to a mixing vessel containing a digester liquid which has been largely depleted of digestible organic materials but containing a similar mineral content as the raw manure, subsequently filtering to remove solids to produce a liquid containing ammonia and reactive organic materials, heating to an elevated range to produce ammonia and kill bacteria, removing the ammonia, cooling the remaining liquid to a digestion temperature. One feature of U.S. Pat. No. 6,521,129 is the control of the ammonia concentration to maintain it below inhibitory levels.
Those in the art recognize that such different operations produce differing waste materials as potential feed material to generate methane. The handling, storage and disposal of poultry litter is becoming more regulated and, resultantly, a financial and management burden to the poultry farmer. What is needed is a method of poultry waste management which addresses such concerns.